The present invention relates to a device controller with power control function, a USB device controller with power control function, and a power control method.
The USB (Universal Serial Bus) standard is typically used to couple various peripheral devices to a computer device that serves as a host device. In order to perform communication on the basis of the USB standard, a host device needs to include a USB host controller while a peripheral device coupled to the host device needs to include a USB device controller. With advances in technologies, the USB standard has been enhanced over time. While the USB 2.0 standard is still the most popular USB standard version used in the market, the USB 3.0 standard has already been developed, and USB 3.0 standard based products are expected to become popular in the market in the near future.
A typical configuration of a USB device controller based on the USB 2.0 standard is shown in FIG. 8. A USB device controller 121 based on the USB 2.0 standard includes a protocol control section 122 and a data buffer 123. The USB device controller 121 receives data from a USB host controller 111 included in a host device, and processes the data using the protocol control section 122. The protocol control section 122 performs data demodulation, header analysis, etc. The processed data is temporarily stored in the data buffer 123, and is then output to a subsequent stage circuit 124, such as a storage device for storing data.
The USB 3.0 standard enables the data buffer to be modified depending on the packet size. Specifically, as shown in FIG. 9, the buffer size allocated to each endpoint (EP) can be modified. An endpoint serves as a control section for a data transfer buffer, and can define the transfer direction, the transfer method, etc. for the buffer allocated to the endpoint. The transfer directions may include OUT transfer in which data is transferred from a host device to a peripheral device and IN transfer in which data is transferred from the peripheral device to the host device. The transfer methods may include bulk transfer, interrupt transfer, etc.
Japanese Unexamined Patent Publication No. 2005-260638 discloses a configuration of a peripheral device based on the USB standard in which a buffer memory is shared by endpoints so as to be allocated to the endpoints. Specifically, this patent reference discloses a configuration in which a buffer memory is shared by a data transmission buffer and a data reception buffer. The patent reference also discloses a process in which the number of packets included in transmission data and the number of packets included in reception data are counted, and the buffer capacity allocated to the data transmission buffer and the buffer capacity allocated to the data reception buffer are modified on the basis of the respective count values.
Furthermore, Japanese Unexamined Patent Publication No. Hei 11(1999)-205412 discloses a low power consumption control method for use in a USB host controller in which the power consumption of the input buffer for receiving data output from a USB peripheral device is reduced when data transfer is not performed via the USB port.